Commercially and clinically, silicone hydrogel contact lenses are a popular alternative to conventional hydrogel contact lenses (i.e., hydrogel contact lenses that do not contain silicon or silicon-containing ingredients). The presence of hydrophobic ingredients, such as siloxanes and other hydrophobic reactive ingredients, in silicone hydrogel contact lens formulations is believed to contribute, at least in part, to the frequent occurrence of clinically ophthalmically unacceptable surface wettabilities associated with the development of new silicone hydrogel contact lenses.
The commercial manufacture of silicone hydrogel contact lenses frequently includes one or more washing steps using volatile organic solvents, such as alcohol, to remove unreacted or partially reacted chemicals, especially hydrophobic chemical ingredients, from the polymerized lens bodies prior to packaging. This is frequently referred to as an extraction process to remove extractable material from the polymerized silicone hydrogel contact lens product. The use of such organic extraction methods are commonly necessary in order to render the lens bodies acceptable for wear in the eye by removing potentially irritation or toxic materials from the lenses, and in some cases to increase the wettability of the lens surfaces. The use of volatile organic solvents facilitates removal of a component of the polymerized silicone hydrogel contact lens that has poor solubility in aqueous solutions or water. However, the use of volatile organic solvents presents safety risks to contact lens manufacturing sites, and can be associated with increased costs of goods. When an organic solvent, such as alcohol, is used to wash a silicone hydrogel contact lens, the contact lens increases in size or swells. For example, it is not uncommon for a pre-washed silicone hydrogel contact lens to have a first diameter, such as about 14.0 mm, and for the same silicone hydrogel contact lens to have a second diameter that is about twice as large as the first diameter after contacting the organic solvent, such as increasing to about 28.0 mm. Subsequent to swelling and washing with organic solvents, such lenses are then washed in aqueous solutions to remove the organic solvent and to reduce the size of the lens back to its original pre-swelled dimensions or dimensions close to its pre-swelled dimensions, for example within 10% of its original dimensions. Therefore, when using organic solvents, it is necessary to design the lens molds, and lens washing devices to take into account the changes in lens size resulting from washing. It is also necessary to process the swollen lenses so that they return to their initial size or close to their original size, such as about 14.0 mm in diameter.
In addition to extracting with volatile organic solvents, a variety of additional manufacturing techniques have been employed to make silicone hydrogel contact lenses having clinically ophthalmically compatible lens surfaces. For example, some silicone hydrogel contact lenses are treated with plasma to form a hydrophilic lens surface; some silicone hydrogel contact lenses are formed from a polymerizable lens formulation containing a hydrophilic polymeric internal wetting agent, such as polyvinyl pyrrolidone (PVP); some silicone hydrogel contact lenses are formed using polar resin contact lens molds instead of non-polar resin contact lens molds, and the lenses do not contain a hydrophilic polymeric internal wetting agent in the polymerizable lens formulation, and are not subject to plasma treatment; and some silicone hydrogel contact lenses are formed in non-polar resin molds and are provided with ophthalmically compatible lens surfaces based on chemical reactivity properties of the chemicals in the polymerizable lens formulation.
Based on the popularity of silicone hydrogel contact lenses, there continues to be a need for new silicone hydrogel contact lenses that are ophthalmically compatible.
Some documents describing silicone hydrogel contact lenses include: U.S. Pat. No. 4,711,943, U.S. Pat. No. 5,712,327, U.S. Pat. No. 5,760,100, U.S. Pat. No. 7,825,170, U.S. Pat. No. 6,867,245, US20060063852, US20070296914, U.S. Pat. No. 7,572,841, US20090299022, US20090234089, and US20100249356, each of which is incorporated in its entirety by reference herein.